1. Field of the Invention
This invention relates generally to the field of semiconductor fabrication. More specifically, the invention relates to new precursors for deposition of metal films on to substrates.
2. Background of the Invention
ALD and CVD are particularly useful techniques for deposition of metal films as compared to other methods of deposition such as physical vapor deposition (PVD) methods like sputtering, molecular beam epitaxy, and ion beam implantation. ALD and CVD can also be used to provide flexibility in the design of manufacturing electronic devices including the potential to reduce the number of processing phases required to provide a desired product. These techniques allow conformal deposition, selective deposition for the deposition of copper, silver, gold and other materials. Suitable processes to form metal films require the identification of relevant precursors requiring strict requirements such as being thermally stable, easily vaporized, reactive, with clean decomposition.
The need for high performance interconnection materials increases as device feature sizes shrink and device density increases. Copper provides an alternative to CVD of aluminum in ultra large scale integrated (ULSI) devices due to its low resistivity (1.67 μΩcm for Cu, 2.65 μΩcm for Al), high electromigration resistance and high melting point (1083° C. for Cu, 660° C. for Al). Its low interconnect resistivity also may allow for faster devices.
Copper precursors are quite volatile and show low deposition temperatures, but are highly, sensitive to heat and oxygen. The latter precursors are rather stable, but are isolated as solids with high melting points and thus require high deposition temperatures. It is common for impurities such as carbon or oxygen to be incorporated during the thermal CVD process when using certain organometallic precursors. For instance, (η 5-C 5H 5)Cu(PMe3) produces copper films leading to incorporation of phosphorus. Moreover, phosphine-containing molecules are disqualified because of their high toxicity. Organic phosphines are very hazardous and PF3 being both hazardous and might lead to undesired phosphorus contamination and fluorine-induced etching/damage. Such chemicals might therefore be subject to strict regulations.
An example of an existing copper precursor includes (1,1,1,5,5,5-hexafluoro-2,4-pentanedionate)CuL ((hfac)CuL), where L is a Lewis base. These types of precursors have been the most studied copper precursors to date because they can deposit copper via a thermal disproportionation reaction. Especially (1,1,1,5,5,5-hexafluoro-2,4-pentanedionate)Cu(trimethylvinylsilane), which has attracted much attention because it is a liquid with reasonably high vapor pressure. Other copper compounds such as (1,1,1,5,5,5-hexafluoro-2,4-pentanedionate)CuL, where L is 1,5-cyclooctadiene (CUD), alkyne or trialkylphosphine, are either solids or liquids with a low vapor pressure. Although (hfac)Cu(trimethylvinylsilane) ((hfac)Cu(tmvs)) has been the most utilized copper precursor, its stability is not satisfactory for the selective growth of copper films with reproducibility. In addition, studies have demonstrated that the chemical vapor deposition reaction of (hfac)Cu(tmvs) under ultra high vacuum conditions produced contamination by carbon and fluorine in the deposited films. Therefore, a precursor with high volatility and stability, which contains no fluorinated ligands, is more desirable for the deposition of copper by CVD.
Copper compounds of acetoacetate derivatives which contain no fluorinated ligands have been previously used as CVD precursors. Although these compounds were reported to be volatile and capable of depositing copper films at low substrate temperatures. The studied acetoacetate derivatives were found to be attractive since they were volatile without employing fluorinated ligands and deposited copper films at temperatures below 200° C. However, these derivatives are solid with high melting points and are incapable of selective deposition of copper. On the other hand, the Cu(I) acetoacetate derivatives deposited copper films at relatively low temperatures via disproportionation reaction. However, few are practical for use as CVD precursors since they are either solids or liquids with a low vapor pressure or they have an extremely low thermal stability (i.e. their decomposition temperature is within a few degrees of their vaporization temperature).
Consequently, there is a need for organometallic precursors to deposit metal film without decomposition of the ligands and without associated toxic by products.